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U.S. Forest Service

Plant of the Week

Pencil Flower, Stylosanthes Biflora, range map. Range map of the Pencil Flower. States are colored green where the Pencil Flower may be found.

Stylosanthes Biflora growing in an open meadow.Stylosanthes Biflora growing in an open meadow.

Image of close up of Stylosanthes bifloraStylosanthes biflora close-up image

Pencil Flower (Stylosanthes biflora)

By Christopher David Benda

Pencil flower is said to be “the cutest flower in all the land.”  It is in the Pea family (Fabaceae).  The genus name “Stylosanthes” comes from the Greek words “stylo” and “anthos,” which collectively mean “style flower.”  This refers to the stalk-like, hollow calyx tube that surrounds the pistil of the flower, which is also why this plant is called pencil flower.  The species name “biflora” means “two-flowered.”  Despite this name, the flowers are often solitary.
This little perennial plant has thin, wiry stems and compound leaves that alternate along the stem.  The leaves are trifoliate, which means they are divided into three leaflets, and each leaflet has a short bristle tip.
It has the characteristic flowers indicative of the Pea family that include three petals: the banner, wings, and keel.  The flowers bloom in the late spring through the summer.   The dark yellow to orange petals are plump and happy, causing passersby to point and exclaim, “oooooh!” when they see them along the trail.   
The flowers are visited by a variety of insects, primarily bees and butterflies, and it is the host plant for the barred sulphur and little sulfur butterflies, as well as at least one type of leaf beetle.  Fertilized flowers produce asymmetrical, indehiscent, slender, beaked pea pods with two segments, though the lowest segment is often sterile.  Thus, just one seed is produced per flower.  Despite the paucity of seeds, they are still a favorite of quail and turkey, perhaps because the seeds remain in the pea pods on the plant (indehiscent), rather than splitting open, releasing the seeds to the ground (dehiscent). 
This common species is variable across its range in the overall hairiness and erectness of the plant, and the number of flowers produced.  Although it is so variable, it is currently considered a single, polymorphic species. It prefers dry woodlands and open rocky glades in the southeastern United States, from Pennsylvania to Florida, and Illinois to Texas.

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